The present invention is directed towards production of urea by integrating ammonia reactant preparation in the urea synthesis process.
At present urea is made from ammonium carbamate according to the reactions:
2NH3+CO2- - - NH2CO2NH4
NH2CO2NH4- - - H2O+H2NCONH2
Most urea is manufactured in connection with synthetic ammonia plants since the necessary carbon dioxide is available from the synthesis gas purification system in front end of the ammonia plant.
A large part of the world""s ammonia production is utilized for the manufacture of urea. Thus, an integrated process for production of urea will have technical and economical advantages. However, with the present technology the production of urea and ammonia takes place in largely independent plants.
The general object of this invention is to provide an improved process for the preparation of urea by the above reaction of carbon dioxide with ammonia to ammonium carbamate and carbamate decomposition to urea product, wherein ammonia production and urea production is combined in a single flow scheme by integrating carbon dioxide and ammonia reactant preparation into synthesis gas purification of the ammonia synthesis.
In accordance with the general object, the invention provides a process for the combined preparation of urea and ammonia reactant by steps of providing ammonia synthesis gas containing carbon dioxide and conversion of the synthesis gas to the ammonia reactant, reacting the ammonia reactant with the carbon dioxide in the synthesis gas to ammonium carbamate and to urea product, which process comprises further steps of:
prior to the conversion of the synthesis gas to the ammonia reactant,
(i) washing the synthesis gas with an aqueous solution of the ammonia reactant and forming a solution being rich in ammonium carbamate;
(ii) removing excess of ammonia reactant from the washed synthesis gas by washing with water and withdrawing an aqueous solution of ammonia reactant;
(iii) purifying the water washed synthesis gas by adsorbing remaining amounts of water and ammonia; and
(iv) passing the purified synthesis gas to the conversion of the gas to ammonia reactant.